Biosynthetic activities of select populations of non-dividing cells in the brain and heart of rodents will be studied to establish limits on the extent of change during aging. Microscopic techniques will be employed to ascertain if sub-populations of dysfunctional cells accumulate during aging or if there is a selective loss of a sub-population of cells in the substantia nigra, locus coeruleus, and myocardium. RNA synthesis and monoamine uptake mechanisms will be studied by autoradiography. Cells containing monoamine stores will be counted by fluorescence microscopy. Axonal flow and protein synthesis will be investigated in the substantia nigra and optic tract. Correlative studies of the effect of aging on RNA synthesis and neuronal-vascular relations may provide a basis for a dysfunctional sub-population of cells. The results of these studies will bear on the theory of aging that non-dividing cells may accumulate more functional damage (e.g. genomic) than cell populations capable of proliferation.